Acoustic Emission Tomography for Characterizing Damage Evolution in Geomaterials Subjected to Complex Stress States

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The discipline of environmental geomechanics deals with the behaviour of earth materials including rocks, soils and concrete that are encountered in a variety of applications related to safe geologic disposal of hazardous materials and structures for their containment, recovery of resources from hydraulic fracturing of gas-bearing shales, injection of greenhouse gases in liquefied form and the recovery of geothermal energy. In all these situations, the geomaterial can either be fractured or damaged during the storage or recovery process. An understanding of the evolution of damage and fracture in geomaterials is particularly important from an environmental perspective since the newly created defects can enhance the migration of hazardous substances from a site to the geosphere. The study of how fluid transport evolves in a medium requires the mapping of damage and fracture creation as the rock is subjected to stress changes. The requested system, which includes the acoustic emission sensors that can operate in high pressure environments and data analysis and processing hardware and software, will be able to construct acoustic tomographic images of damage generation in cylindrical samples of rocks when they are subjected to stress alterations. The research will evaluate, through acoustic tomographic imaging defects generated in 150 mm diameter 300 mm long samples of the heterogeneous Cobourg Limestone, which is an argillaceous rock encountered in a geological horizon considered suitable for a deep geologic repository to store low and intermediate level nuclear waste. The equipment is versatile and the methodologies have immediate applications in all the aforementioned topics with issues critical to the safety and sustainability of the geoenvironment.